Energy gain of weak signal interacting with a strong pump at the director grating in photorefractive hybrid cell is studied. The cell is filled by bent-core cholesteric LC with small twist/bend elastic constants. The director grating is written by the space-charge field penetrating into LC from the photorefractive substrate. Due to a decreased twist/bend elasticity of the LC, the grating magnitude increases causing an increase of the energy gain. Influence of the elastic constants ratio, flexoelectric coefficients, and cholesteric pitch is studied. We show that the gain coefficient can reach higher values in bent-core cholesterics compared to conventional ones.